Two-component developer consisting essentially of toner particles and carrier particles is widely used in image forming apparatuses such as photocopiers, facsimile machines, printers, or multifunction machines having several of those capabilities. Two-component development devices typically include a development roller (i.e., a developer bearer), multiple developer conveyance members to transport developer in the longitudinal direction of the development device, thereby forming a developer circulation channel, and a developer regulator to adjust the amount of developer carried on the development roller upstream from a development range where the development roller faces an image bearer (e.g., a photoreceptor).
Fresh toner is supplied to the two-component development device as the toner inside the development device is consumed in image development. The supplied toner is mixed with the developer in the development device by the developer conveyance member (e.g., conveyance screw), and then the mixed developer is partly supplied to the development roller. While the development roller rotates, the developer regulator (e.g., a doctor blade) disposed facing the development roller adjusts the amount of the developer carried on the development roller, and then the toner in the two-component developer adheres to a latent image formed on the image bearer in the development range.
Typically, at least two developer conveyance members (i.e., first and second conveyance members) are arranged vertically. For example, the first conveyance member (lower conveyance member) serves as a supply screw and supplies developer onto the development roller at a position corresponding to an attraction magnetic pole generated by a magnet roller provided inside the development roller while transporting the developer longitudinally. The second conveyance member (upper conveyance member) serves as a collecting screw and transports the developer separated from the development roller in the direction opposite the direction in which the first conveyance member transports the developer (hereinafter “developer circulation direction).
Developer conveyance channels (first and second conveyance channels) in which the first and the second conveyance members are respectively provided are separated from each other, at least partly, by a partition to prevent the developer from moving to the other conveyance, but can communicate with each other through communication portions in axial end portions. An end of the partition faces the development roller and adjacent to the development roller. The developer is conveyed upward from a downstream end portion of the first conveyance channel to the second conveyance channel and falls under its own weight from a downstream end portion of the second conveyance channel to the first conveyance channel. The developer regulator may be disposed above the development roller.
Arranging the multiple developer conveyance members vertically is widely used in tandem multicolor image forming apparatuses in which multiple development devices are arranged horizontally because this arrangement can make the development device horizontally compact. Compared with an arrangement in which multiple conveyance members are arranged in parallel horizontally, this arrangement can better inhibit the developer that has been used in image development from being supplied to the developer bearer, thus reducing unevenness in image density.
Developer is typically contained in the development device before shipment. To prevent developer from scattering from the development device or adhering to the development roller during transport or storage, various approaches have been tried.
For example, JP-2002-268353-A and JP-4003411-B propose a seal member for separating the development roller from an interior of the development device, that is, a developer containing chamber for containing developer. The seal member is removed before the development device is used at the site of users.
In configurations in which the multiple developer conveyance members are arranged vertically, the area in which the developer bearer faces the developer containing chamber (i.e., first and second conveyance channels) is relatively large, and it is difficult to provide such a seal member.